Method of alloying together with semikilling steel

ABSTRACT

ADMIXED WITH A LADLE OF LIQUID UNKILLED STEEL OF THE SIEMENS-MARTIN (OPEN-HEART) TYPE TO YIELD A MANGANESE CONTENT OF 0.35 TO 1.20% BY WEIGHT IS AN ALLOY HAVING THE FOLLOWING COMPOSITION: 50% TO 85% BY WEIGHT OF MANGANESE (PREFEREABLY 6075%), 2% TO 15% BY WEIGHT OF SILICON, 0.02% TO 0.5% WEIGHT OF TITANIUM, AND THE BALANCE IRON AND THE USUAL IMPURITIES. THIS ALLOY MAY ALSO CONTAIN 0.5% TO 5% ALUMINUM. ON CASTING IN AN INGOT MOLD, A HIGH-QUALITY SEMIKILLED STEEL INGOT IS FORMED WITH AN OXYGEN CONTENT OF THE ORDER OF 0.010 TO 0.015%.

United States Patent ice 3,711,277 METHOD OF ALLOYING TOGETHER WITH SEMIKILLING STEEL Ludwig von Brogdandy, Helmut Richter, and Eckehard Forster, Oberhausen, Germany, assignors to Huttenwerk Oberhausen A.G., O'berhausen, Germany N0 Drawing. Filed July 28, 1969, Ser. N0. 845,501

Claims priority, application Germany, Aug. 1, 1968, P 17 58 750.7 Int. Cl. C21c 7/06; C22c 35/00 US. Cl. 75-129 2 Claims ABSTRACT OF THE DISCLOSURE Admixed with a ladle of liquid unkilled; steel of the Siemens-Martin (open-hearth) type to yield a manganese content of 0.35 to 1.20% by weight is an alloy having the following composition:

50% to 85% by weight of manganese (preferably 60- 2% to 15% by weight of silicon,

0.02% to 0.5% weight of titanium, and

the balance iron and the usual impurities.

This allow may also contain 0.5% to 5% aluminum. On casting in an ingot mold, a high-quality semikilled steel ingot is formed with an oxygen content of the order of 0.010 to 0.015%.

since it avoids piping and yields an ingot which can be rolled with greater perfection and economy, and pro duces rolled bodies of higher quality.

In order to provide overpressure solidification and to obtain a finished product of relatively exact composition, manganese and silicon are added .to the melt.

With steel containing the usual 0.05 to 0.20% by weight of carbon, the melt must contain 0.012% by weight of oxygen in order to form high-quality semikilled steel. Should this percentage of oxygen vary, the ingot will either greatly expand, thereby bringing about surface flaws, or will harden under underpressure with the accompanying disadvantage. In either case, the desired effect will not be reached. It is very diflicult and almost impossible in practice to hold this oxygen at the optimum level (about 0.012% by weight) necessary for simple manufacture of semikilled steel.

It is further known to admix to the melt silicon, manganese and aluminum one after the other, using for example silicomanganese, an alloy of around 20% silicon. 60% manganese, and the balance of iron and the usual impurities. It is often necessary in such a method to make subsequent additions in the mold when the oxygen level is not just right. Such later additions makes for a finished product of dubious quality and of a composition which might well be far from the desired one.

It has been found that when manganese and silicon are used simultaneously to deoxidize a batch of steel, an oxygen level is obtained that is often lower than that which could be reached by silicon and manganese alone and, with customary steel compositions (i.e. more than 0.6% manganese and 0.1% silicon), which appears to be inde- 3,711,277 Patented Jan. 16, 1973 pendent of the silicon concentration and is scarcely dependent upon the steels manganese concentration. It has been, in earlier practice, impossible to set the desired oxygen level only through the use of manganese and silicon, without further additions in the mold.

It is, therefore, the general object of the present invention to provide an improved method of producing semikilled steel ingots.

A more specific object is to provide such a method which overcomes the above-mentioned disadvantages and, thereby, allows a simple, economical and high quality production of semikilled steel.-

A further object of this invention is to provide an improved method of making steel ingots which solidify under overpressure and have an oxygen content in the range of 0.010 to 0.015% by weight without further control of the oxygen content in the ingot mold.

The above objects are attained, in accordance with the present invention, by a method of producing semikilled steel wherein, prior to ingot casting, an alloy of the following composition is admixed with the melt:

50% to 85% by weight manganese (preferably 60% to 2% to 15% by weight silicon,

0 to 5% by weight aluminum,

0.02% to 0.5% by weight titanium, and

the balance iron and the usual impurities.

This alloy is added in a quantity sufiicient to give the melt a manganese content between 0.35 and 1.20% by weight. The melt is then cast in a mold and allowed to solidify under overpressure as is conventional for semikilled steels of the proper composition.

According to another feature of the present invention, the alloy contains 0.5 to 5% by weight of aluminum.

The silicon concentration, in accordance with yet another feature of the invention, is set accordingto the manganese level in the melt. For a melt with between 0.35% and 0.50% by weight of manganese the alloy preferably contains between 9% and 15% of silicon, whereas for a melt with between 0.60% and 1% by weight of manganese the silicon level is held between 3% and 9% by weight in the alloy.

The invention is based on the theory that the titanium content, and generally also the aluminum content, 18 particularly important in the deoxidization of liquid melted steel, having an apparent oxygen-controlling effect which is much greater than their quantities would seem to imply. In particular, the presence of titanium in the alloy allows simple obtention of a low oxygen level in the melt, a level which is much lower than would be obtained without the titanium. The silicomanganese used in the prior-art methods often included some titanium as an impurity; however, since the criticality of this element and the amount present was not recognized, its concentration was largely ignored and haphazard results were, therefore, obtained. The effect of this titanium seems to be that it forms titaniumoxide seed growth on which the manganese silicate can heterogeneously precipitate in grains. The slight amount of deoxidation which may be attributed to the use of titanium cannot account for the effect it has in controlling and establishing the oxygen content of the final ingot.

Thus, as long as the manganese concentration in the melt is held between 0.35% and 1.20% by weight through addition of the alloy of the present invention, the oxygen level in the steel remains in all cases between 0.010% and 0.015% by weight. In other words, the addition of the alloy described above, which itself constitutes a feature of the present invention, automatically regulates the oxygen level in the melt so that the killing process EXAMPLE I A melt from a Siemens-Martin open-hearth furnace is at a temperature of 1600 C. and has, 'by weight, 0.07% carbon and 0.12% manganese. An alloy having the following composition:

64% by weight manganese, 12% by weight silicon,

4% by weight aluminum, 0.08% by weight titanium, and

the balance iron and the usual impurities,

and in quantity equal to 0.65% of the weight of the melt is added to the melt in an ingot casting ladle. This alloy is made by dissolving ferrosilicon and aluminum in melted titanium-containing blast-furnace ferromanganese.

Subsequent to the addition of this alloy, the melt is analysed and has the following ingredients in the following percentages, by weight:

0.11% carbon, 0.41% manganese, and 0.012% oxygen.

This melt is cast without further deoxidation and forms a block with a slightly convex (domed) top indicative of solidification under overpressure.

EXAMPLE II A melt from an open-hearth furnace at 1600 C. has, by weight, 0.07% carbon and 0.12% manganese. An

alloy having the following composition:

64% by weight manganese, 12% by weight silicon,

0.1% by weight titanium, and

the balance iron and the usual impurities and in quantity equal to 0.65% of the weight of the melt is added to the melt. This alloy is made by dissolving ferrosilicon in melted titanium-containing blast-fur- 'nace ferromanganese.

Subsequent to the addition of this alloy the .melt is analyzed and has the following ingredients in the following percentages, by weight:

0.1 1% carbon, 0.41% manganese, and 0.012% oxygen.

EXAMPLE n1 Twenty batches from a 2,280 ton open-hearth blast furnace containing 0.10% to 0.17% by weight carbon and 0.70% to 1.0% by weight manganese are admixed with an alloy consisting of:

70% by weight manganese, 7% by weight silicon,

0.1% by weight titanium 2% by weight aluminum,

6.5% by weight carbon, and

the balance iron and the usual impurities.

Subsequent to the addition of this alloy the melt is analyzed and has the following ingredients in the following percentages, by weight:

0.15% carbon, 0.85% manganese, and 0.012% oxygen.

The mixture is formed in 10 to 20 ton slab molds and are rolled out into shipbuilding plate.

The plate of the invention has between 77% and 80% perfect surfaces, in comparison .with the plate made according to the prior-art system which has between 33% and 37% perfect surfaces. Similarly, the percentage of waste due to piping dropped from 4.6% to 1.9%.

We claim:

1. A method of alloying as well as semikilling a steel melt to produce an ingot of semikilled steel, comprising the steps of:

forming an unkilled liquid steel melt of anopen-hearth steel with a manganese and carbon content selected from the group which consists of 0.07% carbon and 0.12% manganese, and 0.10 to 0.17% carbon and 0.70 to 1.0% manganese;

partially killing said melt by adding thereto an consisting essentially of:

60% to by weight manganese,

3% to 15% by weight silicon,

0.02 to 0.5% by weight titanium,

0 to 5% by weight aluminum, and

balance iron and the usual impurities in a controlled amount and composition so that subsequent to adding said alloy to said melt the latter will contain from 0.35% to 1.20% by weight manganese inversely related to the amount of silicon in said alloy as illustrated in 9% to 15% by weight silicon for 0.35% to 0.60% by weight manganese and 3% to 9% by weight silicon for 0.60% to 1.00% by weight manganese; and thereafter casting said melt into an ingot.

2. The method defined in claim 1 wherein said alloy further consists of 0.5% to 5% by weight aluminum.

alloy References Cited UNITED STATES PATENTS 3,000,731 9/1961 Ototani 75-129 3,131,058 4/1964 Ototani 75l29 3,119,688 1/1964 Rogers et a1 75-134 M X 3,132,936 5/ 1964 Nishida. 7 5-53 OTHER REFERENCES Metals Handbook, 1948 ed., A.S.M., pp. 337-339.

HY LAND BIZOT, Primary Examiner J. E. LEGRU, Assistant Examiner U.S. Cl. X.R. 7557 

